Method of sealing reed switches using infrared energy

ABSTRACT

A method of sealing a magnetic reed in the open end of a tube of infrared absorbing glass uses an elliptical reflector with an infrared energy source at one focal point. The open end of the tube is disposed at the second focal point of the elliptical reflector with the axis of the tube extending along an extension of the line connecting the two focal points. The end of the tube to be sealed is also received within a conical reflector with the tube axis aligned with the axis of the cone of reflection. The conical reflector is moved along the axis of the tube as the glass softens to form the seal so as to concentrate the infrared energy on the top of the seal.

O United States Patent [151 3,660,064 Rohde 1 May 2, 1972 54 METHOD OFSEALING REED 3,537,276. 11 1970 SWITCHES USING INFRARED ENE 3,469,0619/1969 RGY 3,522,407 8/1970 [72] Inventor: Terry L. Rohde, SchillerPark, Ill. 3,523,777 8/1970 Petersen et al. ..65/59 [73] Assignee: C. P.Clare & Company, Chicago, Ill. Primary Examiner Frank w. Miga I [22]Filed: Jan. 29, 1970 Alt0rneyMason, Kolehmainen, Rathburn & Wyss [21 1Appl. N0.Z 6,778 57 ABSTRACT Related U.S. Application Data A method ofsealing a magnetic reed in the open end of a tube of infrared absorbingglass uses an elliptical reflector with an [62] DlVlSlOn of Ser. No.698,471, Jan. 17, 1968, Pat- N infrared energy source at one focalpoint. The open end ofthe 351841 tube is disposed at the second focalpoint of the elliptical reflector with the axis of the tube extendingalong an exten- U.S. 54, ign of the line connecting the two focal pointsThe end of the 12 tube to be sealed is also received within a conicalreflector [51] Int. Cl ..C03c 29/00, COlc 27/02 with the tube axisaligned with the axis of the cone of reflec- [58] Field of Search 65/59,DIG. 12, 40, 156, 154, tion. The conical reflector is moved along theaxis of the tube 65/DlG. 4 as the glass softens to formthe seal so as toconcentrate the infrared energy on the top of the seal. [56] ReferencesClted 3 Claims, 5 D g Figures UNITED STATES PATENTS 3,155,478 ll/l964O'Brien ..65/DlG. 12

METHOD OF SEALING REED SWITCHES USING INFRARED ENERGY This applicationis a division of a prior application, Ser. No. 698,471 filed Jan. 17,1968, now U.S. Pat. No. 3,518,411.

This invention relates to a method of and apparatus for carrying outinfrared heating and, more particularly, to a method of and apparatusfor using infrared heat to make sealed magnetic reed switches.

' The development of low cost, high energy infrared sources coupled withthe availability of glass having very high energy absorption in theinfrared range has made it possible to make sealed magnetic reedswitches in less timethan required in the past. The glass tube used toform the switch housing is made of infrared absorbing or green" glassand, following the insertion of the magnetic reed into an open end ofthe housing, the glass tube is subjected to radiation in the infraredrange to soften or melt the glass and seal the reed in the end of thetube.

In order to produce the seal as quickly as possible and to utilize thegenerated infrared energy as eificiently as possible,

' it has been proposed to place the energy source at one focal point ofan elliptical reflector, to place the glass to be heated at a secondfocal point, and to use a spheroidal back reflector spaced from theglass tube and the elliptical reflector. This arrangement focuses thegenerated infrared energy on the glass to be heated in proximity to thepoint at which the glass-tometal seal is to be formed. However, it isdesirable to manufacture the reed switches using automatic machinery andcontinuous assembling techniques, and the focusing arrangement describedabove requires control of a rather large number of somewhat criticaldimensions. Frequently, this control cannot be adequately exercised'inan assembling machine. In addition, this arrangement has sometimesresulted in a blowout or the distortion of the last glass seal to beformed due to heatinduced expansion of the atmosphere sealed within thehousing of the switch.

Accordingly, one object of the present invention is to provide a new andimproved method of an apparatus for carrying out infrared heating.

Another object is to provide an infrared heating apparatus using focusedenergy in which the number of critical dimensions is substantiallyreduced.

A further object is to provide a new andimproved apparatus for makingsealed reed switches in which the axis of the glass tube forming thehousing of the switch is disposed along the axis of an ellipticalreflector.

A further object is to provide a new and improved method of usinginfrared heat to form glass-to-metal seals in reed switches that avoidsor reduces the number of blowouts" previously encountered in switchproduction.

A further object is to provide a method of using infrared heat to formsealed reed switches that is adapted for use in continuous assemblingoperations.

In accordance with these and many other objects, an embodiment of theinvention comprises an infrared heating apparatus for use in the formingof the glass-to-metal seals in reed switches which includes a highenergy infrared source placed at the first focal point of an ellipticalreflector to focus the infrared energy at a second focal point at whichis disposed the open end of a glass tube in which a magnetic reed ispositioned. The glass tube, which is formed of infrared absorbing orgreen" glass, is positioned within a conical reflector extending throughan opening on the axis thereof so that the axis lies along a lineintersecting the two focal points of the elliptical reflector. Thisarrangement focuses the infrared energy on the glass tube in the area inwhich the glass-to-metal seal is to be formed and possesses theadditional advantage that a minimum of shadow forming structure isinterposed between the infrared source and the glass to be heated. Toprevent the occurrence of blowouts as the glass begins to soften and toflow inwardly toward the magnetic reed to form the seal, the conicalreflector is moved toward theelliptical reflector so that the infraredenergy is focused on or is capable of reaching only the top surface ofthe glass forming seal. By shifting'the glass tube and the reed to besealed therein.

reflector axially relative to the axis of elongation of the glass, theapplication of infrared energy to the area of the seal is con-, trolledwithout disturbing the predetermined positions of the Many other objectsand advantages of the present invention will become apparent fromconsideringthe following. detailed description in conjunction with thedrawings in which:

FIG. 1 is a top plan view of an infrared heating assembly previouslyused;

FIG. 2 is a side elevational view of the shown in FIG. 1;

FIG. 3 is a schematic elevational view in partial section illustratingan infrared heating assembly embodying the present invention and shownin the position occupied at thejbeginningof the heating operation; I

FIG. 4 is a view similar to FIG. 3 illustrating the condition of theheating assembly at the end of the heating operation; and

FIG. 5 is a top plan view taken along line 5-5 in FIG. 3.

Referring now more specifically to FIGS. 1 and 2 of the drawings,therein is illustrated a known arrangement for using infrared energy toform glass-to-metal seals in the process of manufacturing sealedmagnetic reed switches. The reed switches are manufactured usingmagnetic reeds (not shown), and a tube 12 of glass having veryhighinfrared energy absorption, such as green" glass. The reeds areinsertedin the open ends of the tubes 12, and the glass at the ends ofthe tube is softened or melted to flow into engagement with the insertedreeds to form a glass-to-metal sea]. In the apparatus 10, a highintensity infrared energy source 14 is disposed at a first focal pointof an elliptical infrared reflector 16 so that energy impinging on thereflector 16 is, focusedon a second focal point indicated at 18. Aspheroidal back reflector 20 is spaced at'the other side of the secondfocal point 18 fromthe elliptical reflector 16 to collect radiationpassing beyond the focal point 18 and to return this energy to thevicinity of the focal point 18.

To insure the maximum transfer of energy from the infrared energy source14 to thetube 12, the tube is disposed at the second focal point 18 withthe axis of elongation of the tube 12 extending perpendicular to theaxis of the reflector16, i.e., a line connecting the two focal points ofthe reflector 16. By efficiently collecting and utilizing theinfraredenergy from the source 14, the time required to melt or soften the glassof the tube 12 disposed at the focal point 18 to the extent that itflows into engagement with the inserted magnetic reed (not shown) andthus forms the magnetic seal, is substantially reduced. Seals producedby the apparatus 10 require on the order of 4 seconds.

However, in attempting to carry out the automatic assembly andmanufacture of reed switches using a heating apparatus of the generalnature of the apparatus 10, it has been determined that it is difficultto achieve the full advantages of this system because of the number ofsomewhat critical dimensions that must be maintained for maximum energytransfer. As an example, it is necessary to control the distance A fromthe reflector 16 to the center line or axis of the glass tube 12, thedistance B from the back reflector 20 to the center. line of the glasstube 12, the distance C from the center line or axis of the reflector 16to the end of the glass tube 12, the distance D from the axis or centerline of the back reflector 20 to the end of the glass tube 12, thedistance E from the center line of the reflector 16 to the axis of thetube 12 measured in a direction at right angles to the distance C, and'the distance F from the center line of the back reflector 20 to the axisof the glass tube 12 measured in a direction perpendicular to thedistance D. Further, it is necessary to control the separation G of thetwo parts 20A and 20B of the back reflector 20, which separation lies inthe shadow area of the reflector to permit variations in the focal pointof this reflector 20. If all of these seven dimensions are not carefullycontrolled, the maximum transfer of energy from the source 14 to theglass tube 12 is not obtained, and in addition, uneven heating of theend portion of the glass tube 12 occurs with the result that anobjectionable nonsymheating assembly metrical seal between the glasstube 12 and the magnetic reed occurs.

FIGS. 3-5 of the drawings illustrate an infrared heating apparatus whichis indicated generally as 30 and which, embodies the present invention.The apparatus 30 is capable of producing glass-to-metal seals in reedswitches in a shorter period of time and is better adapted for use inautomatic assembling and manufacturing equipment in requiring thecontrol of a substantially smaller number of critical dimensions thanthe assembly previously used. The apparatus 30 is also capable ofreducing or avoiding the oxidation of the reeds and the occurrence ofblowouts during fabrication of the switches and of improving sealsymmetry;

The apparatus 30 is used to make sealed magnetic reed switchesconsisting of a pair of magnetic reeds 32 formed of a suitable materialsuch as nickel-iron alloys which are sealed in the open opposite ends ofa glass tube 34. The glass forming the tube, which is sometimes calledgreen glass, contains a small amount of iron oxide to provide a veryhigh energy absorption in the infrared region of around one to 4 micronswave-length. This glass has a working point of around 1,780 E, asoftening point of 1,160 E, and an annealing point of 8 10 F. Bysubjecting the glass of the tube 34 to infrared energy, the glass can besoftened or melted to form a seal with the magnetic reeds 32.

The apparatus30 for making the sealed switches includes an ellipticalreflector 36 at one focal point of which an infrared energy source 38 isdisposed. The infrared source 38 can comprise a 650-1000 watt quartziodine lamp produced by Argus Engineering Company of Hopewell, NewJersey. The apparatus also includes a back reflector 40 having areflecting surface 42 which is conical or of conic section and which inone embodiment of the present invention comprises a reflecting surfaceof an 82 right circular cone. The axis of the reflecting surface 42 isaligned or coincident with the axis of the elliptical reflector 36 orlies on the line connecting the two focal points of the ellipticalreflector 36.

When a glass-to-metal seal is to be made, a magnetic reed 32 is insertedinto one open end of the glass tube 34 and held in position by a holdingmeans 44' of any suitable construction. The glass tube 34 is also heldin any suitable known holding or chuck means in such a position that theaxis of elongation of the tube 34 generally coincides with the axis ofthe reflector 36 with the end of the tube 34 in which the seal is to bemade disposed within the conical reflector 42. The end of the tube 34that is to be softened to form the seal is disposed at the second focalpoint of the reflector 36.

When the infrared energy source 38 is energized, the energy emittedtherefrom is directly transmitted to and focused by the reflector 36 andthe conical reflecting surface 42 of the back reflector 40 on the openend of the tube 34 to be absorbed by the glass at the upper end of thetube 34 so that it becomes softened and flows inwardly toward thereduced diameter portion of the reed 32 to form a seal therewith. Sincethe only structure interposed between the reflector 36 and the portionof the glass tube 34 to be heated is the upper end of the reed 34 andthe very small transverse dimension of the holding means 44, the shadowarea is very small, and the energy transmission from the source 38 tothe upper end of the glass tube 34 is quite efficient. Further, theconical reflecting surface 42 serves to evenly distribute the heataround the upper end of the glass tube 34 to aid in the production of asymmetrical seal. In addition, the transmission of infrared energy toareas remote from the area in which the seal is to be formed isprevented. This avoids the heating of the portion of the reed 32 locatedwithin the tube 34 and thus avoids its oxidationf To provide means forfurther insuring the symmetry of the seal and to avoid blowouts, meansare provided in the apparatus 30 for shifting the position of thereflector 40. More specifically, this arrangement, which can be of anysuitable construction, is illustrated as comprising a generally Y-shapedlever 46 pivoted at a point 48 and having two bifurcations or arms 46Aand 468 with rounded portions which bear against a lower surface of thereflector 40. The other end of the lever 46 is connected to a motivepower source or solenoid 50. The lever 46 normally occupies the positionillustrated in FIG. 3 at the initiation of the infrared heatingoperation.

When the glass at the top of the tube 34 starts to soften and flowtoward the magnetic reed 32, the power source or solenoid 50 isenergized to pivot the lever 46 in a counterclockwise direction aboutthe pivot point 48. This shifts the reflector 40 upwardly from theposition shown in FIG. 3 to the position illustrated in FIG. 4. Bymoving the conical reflecting surface 42 toward the energy source 38,the upper end of the glass tube 34 in which the seal is to be formedremains at'the second focal point of the reflector 36, but the energyreflected off the conical surface 42 is concentrated at the uppersurface of the seal in formation, as indicated at 52 in FIG. 4, so thatI the greatest quantity of heat is concentrated at the point at whichthe glass of the tube 34 must be rendered most molten to flowinto'contact with the reed 32 to form the seal. Further, the heating ofthe glass tube 34 in the area immediately below the seal is somewhatreduced. If the seal being formed in the switch is the second seal sothat the volume within the glass tube 34 is sealed from communicationwith the atmosphere, the concentration of heat at the end of the seal atthe point-52 and the removal of heat from the lower portion of the glasstube34 prevents excessive heating of the sealed atmosphere within theswitch, and thus tends to reduce .blowouts. In addition, by moving theconcentration of heat upwardly to the general area indicated by 52, thesymmetry of the finished seal is improved and heating of the part of thereed 32 within the tube 34 is reduced. The solenoid or drive means 50can be released to restore the reflector 40 to the position illustratedin FIG. 3 at the conclusion of the formation of the seal and conditionthe apparatus 30 for forming the seal on the next switch. Seals producedby the apparatus 30 require on the order of 2 secondsusing an energysource 38 of the same power as the source 14.

The apparatus 30 is well suited for automatic assembling operationsbecause only three dimensions must be accurately controlled to insureefiicient' and accurate heat application and distribution. Morespecifically, the center line or axis of the elongated glass tube 34relative to the center line or axis of the elliptical reflector 36 mustbecontrolled in two mutually perpendicular directions, and the spacingof the reflector 36 and the conical reflector 40 must be controlled.Thus, only these three dimensions must be controlled to insure accurateand efficient heat distribution and concentration. A fourth dimension,namely the position of the end of the glass tube 34 along the axis ofthe conical reflecting surface 42, can becontrolled in the mannerdescribed above to improve the symmetry of the seal and preventblowouts."

Although the present invention has been described with reference to asingle illustrative embodiment thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art that will fall within the spirit and scope of theprinciplesof this invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

l. A method of sealing a metal element in an open end of a tube ofglass, which method comprises the steps of inserting the elementpartially'within the tube through the open end,

applying heat to an area of the glass of the tube adjacent the i openend of the tube until the glass starts to soften and flow toward theelement to start the seal, and producing a displacement between the tubeand the area of application of the heat to move the area of applicationof the heat to the glass toward the end of the tube as the glass softensso that the heat is applied to an area at the outer end of the seal. 2.A method of sealing a metal element in an open end of a tube of infraredabsorbing glass, which method comprises the steps of v toward the end ofthe tube as the seal startsto form to concentrate the infrared energy onthe that forms the top of the seal.

3. The method set forth in claim 1 including a heat applying I area ofthe glass means in which the step of producing a displacement includesthe step of producing relative movement between the glass tube and theheat applying means.

1. A method of sealing a metal element in an open end of a tube ofglass, which method comprises the steps of inserting the elementpartially within the tube through the open end, applying heat to an areaof the glass of the tube adjacent the open end of the tube until theglass starts to soften and flow toward the element to start the seal,and producing a displacement between the tube and the area ofapplication of the heat to move the area of application of the heat tothe glass toward the end of the tube as the glass softens so that theheat is applied to an area at the outer end of the seal.
 2. A method ofsealing a metal element in an open end of a tube of infrared absorbingglass, which method comprises the steps of inserting the elementpartially within the tube through the open end, directing infraredenergy on an area adjacent the top of the tube until the glass softensand starts to flow toward the element to form a seal, reflectinginfrared energy onto an area adjacent the top of the tube to supplementthe directed energy, and producing relative movement between the tubeand the reflected energy to move the reflected infrared energy towardthe end of the tube as the seal starts to form to concentrate theinfrared energy on the area of the glass that forms the top of the seal.3. The method set forth in claim 1 including a heat applying means inwhich the step of producing a displacement includes the step ofproducing relative movement between the glass tube and the heat applyingmeans.